The only type of life we know is based on complex carbon chemistry. Is this the only option possible? Can we imagine a silicon-based life?
Life as we know it, we are dealing with a carbon-based one, which uses water as a medium for conducting numerous chemical reactions and oxygen to generate energy during metabolic processes.All forms of life on our planet share the same biochemistry. Starting from this last sentence I would say that this is the only kind of life possible in the universe. But that would be a kind of "carbonocentrism". A limited vision, of what it would be possible in another corner of the universe?
In similar conditions the laws of physics are the same wherever we go in the universe. Starting from this statement means that we can use what science tells us about chemical reactions studied on Earth.
So, knowing that silicon is about 140 times more abundant than carbon, how come that life-forms here on Earth, are not based on this item?
It's all about elementary chemistry. Carbon and silicon are in the same column of the Table of Mendeleev and their atoms have the last layer the same number of electrons: 4. Both elements can be combined in very complex chemical compounds, which would entitle us to assume the possibility of life based on silicon. Not quite so. To complete the valence electron layer where for carbon is needed only four electrons, which makes carbon-carbon type bonds to be extremely strong. Remember diamond, the hardest known material.
"carbon"
The fact that carbon-carbon bonds are so strong, gives the chemical combinations based on carbon the ability not to be affected by the water's presence. As for silicon, situation is different . It is true, as I said above, we have here too, four electrons on the last electronic layer. But to fill it we need 14 (maximum possible number of electrons on the last layer of silicon atom is 18).
This makes the silicon-silicon bonds to be less powerful, they become unstable in the presence of plenty of fluids, especially in the presence of water.
Another problem with silicon refers to "retention" to achieve its double and triple bonds, which limits the range of silicon-based chemicals. I will not insist on this, but i emphasize that very ability of carbon to achieve molecular chains no matter how long, is one of the important features that leads to life.
Another problem is related to oxygen. This is a widespread chemical in the universe, a highly reactive component. When carbon reacts with oxygen it produces a gas, carbon dioxide.
This gas combines leasily, in turn, with other chemical compounds, and the bond between carbon and oxygen can easily break in biochemical processes, such as the photosynthesis.
"silicon"
With silicon the situation is quite different. Same as carbon, it combines easily with oxygen, only the silicon dioxide resulting from the reaction is a solid one, known to us all as quartz. Imagine some beings breathing out silicon powder. Chemically, the silicon dioxide is a stable compound that interacts poorly with other substances. Still any hopes?
"silicon"
With silicon the situation is quite different. Same as carbon, it combines easily with oxygen, only the silicon dioxide resulting from the reaction is a solid one, known to us all as quartz. Imagine some beings breathing out silicon powder. Chemically, the silicon dioxide is a stable compound that interacts poorly with other substances. Still any hopes?
Here are three problems that make impossible the emergence of life based on silicon on a planet as Earth. What about in other corners of the universe?
For example we could imagine a planet whose surface temperature reign of several hundred degrees, a temperature where carbon-based bonds would break.
Silicon compounds will last very well, to give you an example, we will remember silicone oils (which can be viewed as silicon-based organic substances).
These are used for lubrication of mechanisms operating at high temperatures, just because of their capacity to resist strongly at heated environments. We dare here a hypothesis.
Yes, it would be possible, somehow, somewhere occur silicon life forms on planets with temperatures above 400 degrees Celsius.
"hypothetical silicon based life-forms"
What is the secret of LIFE?
But they will remain forever in the very primitive life and will require much imagination to assume complex forms of life based on silicon. Our argument is the same: silicon can not easily achieve complex macromolecules. We have a clear information in this regard. As we know, it is likely that organic molecules, building-blocks of life, have appeared in the interstellar environment. There we have already found 83 kinds of complex molecules based on carbon and only 7 based on silicon.
"hypothetical silicon based life-forms"
We say as a temporary conclusion that alien life, that we will one day meet, will be based on carbon. I say "temporary conclusion" simply because sometimes it happens that reality goes beyond our imagination . And in science all that matters is reality!
What is the secret of LIFE?
I list some of the features that should satisfy a certain chemical element to form the basis of living matter.
1. Underlying element of life should be sufficiently abundant on the planet, to facilitate prebiotics chemical reactions.
2. It must be able to participate in bio-geo-chemical cycles in the whole biosphere, atmosphere, oceans, to foster the development of ecosystems.
3. The atoms of living matter must form at least three chemical bonds in order to achieve a system of biopolymers.
4. Chemical bonds between atoms that make up living matter must be sufficiently stable to prevent the created structure to be destroyed to a small variations of external conditions.
So.. only carbon can form the basis for life as we know it. But let's make a step further. We need carbon and what else? Of course.. we need liquid water. Let's name a few water features, which are indispensable for carrying out biological processes.
1. Liquid water has the advantage that can help the living forms, dissolving components, carrying the key molecules and activating chemical reactions.
2. Water is a universal solvent. Hydrogen atoms in its composition can be linked easily with other molecules.
3. Due to its structure, water allows the construction of enzymes, amino acid molecules that catalyze chemical reactions . In the absence of water and enzymes, could not achieve metabolic reactions from the cells.
4. Water has a very important property: the highest specific heat of all known substances. In other words, it takes a lot of heat to slightly rises the temperature of water. This water quality is that it can be a great heat regulator.
The universe is so wonderful and complex that somewhere else, randomly, life-forms would be born in conditions that we, terrestrial, would consider truly hostile.
by "environment clean generations"
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